Biodiversity and ecosystem multifunctionality

Biodiversity loss can affect ecosystem functions and services. Individual ecosystem functions generally show a positive asymptotic relationship with increasing biodiversity, suggesting that some species are redundant. However, ecosystems are managed and conserved for multiple functions, which may require greater biodiversity. Here we present an analysis of published data from grassland biodiversity experiments, and show that ecosystem multifunctionality does require greater numbers of species. We analysed each ecosystem function alone to identify species with desirable effects. We then calculated the number of species with positive effects for all possible combinations of functions. Our results show appreciable differences in the sets of species influencing different ecosystem functions, with average proportional overlap of about 0.2 to 0.5. Consequently, as more ecosystem processes were included in our analysis, more species were found to affect overall functioning. Specifically, for all of the analysed experiments, there was a positive saturating relationship between the number of ecosystem processes considered and the number of species influencing overall functioning. We conclude that because different species often influence different functions, studies focusing on individual processes in isolation will underestimate levels of biodiversity required to maintain multifunctional ecosystems.     

Melanoma biology and new targeted therapy

Melanoma is a cancer that arises from melanocytes, specialized pigmented cells that are found predominantly in the skin. The incidence of melanoma is rising steadily in western populations--the number of cases worldwide has doubled in the past 20 years. In its early stages malignant melanoma can be cured by surgical resection, but once it has progressed to the metastatic stage it is extremely difficult to treat and does not respond to current therapies. Recent discoveries in cell signalling have provided greater understanding of the biology that underlies melanoma, and these advances are being exploited to provide targeted drugs and new therapeutic approaches.     

定数截尾数据缺失场合下Weibull分布的Bayes统计分析

当寿命分布为Weibull分布时,本文给出了定数截尾数据缺失场合下各种参数的Bayes估计,并且给出了它们与极大似然估计的模拟比较.     

分子印迹-流动注射分子荧光法测定水中双酚A的研究

以双酚A(BPA)为模板分子,以丙烯酰胺为功能单体,季戊四醇三丙烯酸酯为交联剂,采用悬浮聚合法,在水性体系中制备了表面带孔的分子印迹聚合微球( MIPM),制备的BPA分子印迹聚合微球( BPA - MIPM)吸附平衡时间为110 min,饱和吸附量为34.38 μmol·g-1.BPA - MIPM以苯酚为竞争分子,分离因子达到22.88;制备的MIPM具有良好的选择吸附性能和良好的再生性能.以BPA - MIPM为分子识别物,基于在pH为1的酸性介质中,β-环糊精对双酚A荧光强度的增强作用,建立测定BPA的分子印迹-流动注射分子荧光法.测得BPA在0.1～100 μg·L-1线性范围内具有很好的相关性,相关系数r为0.9993,相对标准偏差(20μg·L-,n=11)为0.79％,检出限为0.08 μg·L-,用该方法测水中BPA的加标回收率为98.6％ ～ 103.9％,结果较好.     

Cell-to-cell spread of HIV permits ongoing replication despite antiretroviral therapy

Latency and ongoing replication have both been proposed to explain the drug-insensitive human immunodeficiency virus (HIV) reservoir maintained during antiretroviral therapy. Here we explore a novel mechanism for ongoing HIV replication in the face of antiretroviral drugs. We propose a model whereby multiple infections per cell lead to reduced sensitivity to drugs without requiring drug-resistant mutations, and experimentally validate the model using multiple infections per cell by cell-free HIV in the presence of the drug tenofovir. We then examine the drug sensitivity of cell-to-cell spread of HIV, a mode of HIV transmission that can lead to multiple infection events per target cell. Infections originating from cell-free virus decrease strongly in the presence of antiretrovirals tenofovir and efavirenz whereas infections involving cell-to-cell spread are markedly less sensitive to the drugs. The reduction in sensitivity is sufficient to keep multiple rounds of infection from terminating in the presence of drugs. We examine replication from cell-to-cell spread in the presence of clinical drug concentrations using a stochastic infection model and find that replication is intermittent, without substantial accumulation of mutations. If cell-to-cell spread has the same properties in vivo, it may have adverse consequences for the immune system, lead to therapy failure in individuals with risk factors, and potentially contribute to viral persistence and hence be a barrier to curing HIV infection.     

Genome sequence and analysis of the tuber crop potato

Potato (Solanum tuberosum L.) is the world's most important non-grain food crop and is central to global food security. It is clonally propagated, highly heterozygous, autotetraploid, and suffers acute inbreeding depression. Here we use a homozygous doubled-monoploid potato clone to sequence and assemble 86% of the 844-megabase genome. We predict 39,031 protein-coding genes and present evidence for at least two genome duplication events indicative of a palaeopolyploid origin. As the first genome sequence of an asterid, the potato genome reveals 2,642 genes specific to this large angiosperm clade. We also sequenced a heterozygous diploid clone and show that gene presence/absence variants and other potentially deleterious mutations occur frequently and are a likely cause of inbreeding depression. Gene family expansion, tissue-specific expression and recruitment of genes to new pathways contributed to the evolution of tuber development. The potato genome sequence provides a platform for genetic improvement of this vital crop.